This disclosure generally relates to a fuel tank isolation control valve. In particular, this disclosure is directed to an evaporative emission control system including a fuel tank isolation control valve to control the flow of fuel vapor from a fuel tank of a vehicle.
It is believed that prior to legislation requiring vehicles to store hydrocarbon vapors that are generated when refueling a vehicle, a simple orifice structure was used to maintain a positive pressure in a fuel tank to retard vapor generation. It is believed that such orifice structures could no longer be used with the advent of requirements controlling onboard refueling. It is believed that, on some vehicles, the orifice structure was simply deleted, and on other vehicles, the orifice structure was replaced with a diaphragm-actuated pressure relief valve.
It is believed that it is necessary on some vehicles to maintain an elevated pressure in the fuel tank to suppress the rate of fuel vapor generation and to minimize hydrocarbon emissions to the atmosphere. It is believed that under hot ambient temperature conditions or when the fuel is agitated, e.g., when a vehicle is operated on a bumpy road, the amount of fuel vapor generated can exceed the amount of fuel vapor that can be purged by the engine. It is believed that a purge canister can become hydrocarbon saturated if these conditions occur and are maintained for an extended period. It is believed that such a hydrocarbon saturated purge canister is unable to absorb the additional fuel vapors that occur during vehicle refueling, and that hydrocarbon vapors are released into the atmosphere.
It is believed that there is a need to provide a valve that that overcomes the drawbacks of orifice structures and diaphragm-actuated pressure relief valves.
The present invention provides a system for controlling evaporative emissions of a volatile fuel. The system includes a fuel vapor collection canister, an isolation valve, and a fuel tank. The isolation valve includes a housing defining a chamber, a diaphragm movable with respect to the housing between a first configuration and a second configuration, and a coil spring biasing the diaphragm toward the first configuration. The housing includes an interior partition that defines an aperture and separates the housing into first and second sections, a first port that is in fuel vapor communication with the fuel vapor collection canister, and a second port. In the first configuration, the diaphragm occludes the aperture, divides the chamber into three sub-chambers, and substantially prevents fuel vapor flow between the first and second ports. In the second configuration, the diaphragm divides the chamber into two sub-chambers and permits generally unrestricted fuel vapor flow between the first and second ports. The coil spring includes a first end that engages the housing and a second end that engages the diaphragm. The fuel tank is in fuel vapor communication with the second port of the isolation valve.
The present invention also provides a fuel tank isolation valve. The fuel tank isolation valve includes a housing defining a chamber, a diaphragm movable with respect to the housing, and a resilient element. The housing includes a first port and a second port. And the resilient element biases the diaphragm toward a first configuration that divides the chamber into three sub-chambers and substantially prevents fluid flow between the first and second ports.
The present invention also provides a method of controlling fuel vapor flow between an evaporative emission space of a fuel tank and a fuel vapor collection canister. The method includes providing a fuel tank isolation valve, moving the diaphragm to a first configuration in response to a second pressure level at a second port, and moving the diaphragm to a second configuration in response to a first pressure level at a first port. The fuel tank isolation valve includes a housing defining a chamber, a diaphragm movable with respect to the housing between the first configuration and the second configuration, and a resilient element biasing the diaphragm toward the first configuration. The housing includes a first port that is adapted for fuel vapor communication with the evaporative emission space of the fuel tank and includes a second port that is adapted for fuel vapor communication with the fuel vapor collection canister. The first configuration divides the chamber into three sub-chambers and substantially prevents fluid flow between the first and second ports. The second configuration divides the chamber into two sub-chambers and permits generally unrestricted fluid flow between the first and second ports. The first pressure level is above atmospheric pressure, and the second pressure level is below atmospheric pressure.